It is generally known that an internal combustion engine is controlled and monitored with an engine control device (control device). The internal combustion engine is equipped for this purpose with an injection system, for example with a common rail or a pump-nozzle injection system. In order to inject fuel into the various cylinders of the internal combustion engine, a fuel injector is arranged on each individual cylinder. Piezo-electric injectors are usually used, in particular, also to be able to carry out a multiple-injection with pre-injections and post-injections, since this type of injector not only permits rapid switching times, thereby allowing very small injection quantities to be controlled, but also has sensory properties which can be used for controlling positions.
Furthermore, it is known that in engines, in particular with a relatively large number of cylinders, a plurality of cylinders are combined to form one bank. Depending on the bank system, the control device can actuate a different number of injectors simultaneously. For example, in a single-bank system one fuel injector is actuated and in a two-bank system two fuel injectors are actuated simultaneously. The actuation is carried out by means of correspondingly embodied electric output stages which are arranged in the control device. The output stages generate voltage pulses/current pulses for the injectors, which voltage/current pulses are converted into a mechanical movement in the injectors and in the process they open or close to a greater or lesser degree the corresponding injection valve in order to inject fuel into a cylinder of the internal combustion engine.
Furthermore it is known that for one injection cycle of a cylinder a plurality of consecutive injection pulses are generated successively and the injection pulses are carried out with the same clock cycle.
For physical reasons, a fuel injection can be injected only within one specific rotational angle of the crankshaft of the internal combustion engine. The resulting angular spread for an injection is also referred to as a segment. Depending on the number of cylinders of the bank system used, different segments for the fuel injection arise given uniform distribution. A segment S is usually calculated according to the following formula:S[° CA]=720[° CA]/number of cylinders×number of banks.
Since the segments follow one another in terms of timing, the control device can only actuate the segments sequentially. This means that in known injection systems the segments are constant and cannot be changed. This has the disadvantage that an injection pulse which would lie outside the predefined segment cannot be carried out. In particular, for example, during the regeneration of a particle filter of a diesel engine, it is not possible for very retarded post-injections to be carried out outside the segment. However, this may be necessary in order to heat the particle filter by means of injected, unburnt fuel for the post-injection. Furthermore, such a post-injection should not lead to an increase in torque. It has not been possible to solve this problem hitherto in the known prior art.
The document DE 10 2006 004 281 A1, which was published after the priority date of the document in question here, describes a device and a method for controlling the metering of fuel into an internal combustion engine. In this context, in the case of a first angular position of a crankshaft or camshaft first variables are calculated in order to control at least a first partial injection, and in the case of a second angular position at least a second variable is calculated in order to control a second partial injection. Furthermore, a limiting value is predefined and the at least one second variable is limited to this limiting value.
Document DE 39 23 479 A1 discloses a method for carrying out sequential injection processes, in which, when predefined injection angles are reached, crankshaft incremental signals are generated and these incremental signals are counted in relation to a reference signal. As soon as a predefined injection angle is reached, the assigned injection process is carried out. With the described method it is possible to define the start of injection angle and end of injection angle precisely. The start of injection angle can be read out from a characteristic diagram as a function of the rotational speed and injection period.
Document DE 101 52 903 B4 describes a method for calculating injection time periods for an internal combustion engine which can be operated in a homogenous mode at certain times and in a stratified mode at certain times, wherein in the stratified mode the injection time period is calculated repeatedly for each cylinder per working cycle (720° CA) of the internal combustion engine, and wherein in the homogenous mode the injection time period for each cylinder is calculated only once per working cycle of the internal combustion engine.
Document DE 101 04 252 C1 describes a method for controlling an internal combustion engine according to which an action which has to be triggered earlier by a defined time period is to be carried out at a defined crankshaft angle. The time of the defined crankshaft angle is extrapolated as a function of the current crankshaft angle and the defined time period. The action is triggered if the extrapolated defined time differs from the current time by the defined time period.
Document DE 10 2004 014 369 A1 proposes a method for controlling an internal combustion engine. An ignition of a spark plug and an injection of fuel are intended to occur at certain crankshaft angles. This action has to be started with a sufficient lead time. The starting times are calculated taking into account the lead time.